1. Field of the Invention
The present invention relates to a surface defect inspection device and a shading correction method therefor, and, more specifically, relates to a method in which shading correction is performed for a line sensor in an extraneous substance detecting optical system in a semiconductor wafer extraneous substance inspection device, in which an extraneous substance is inspected by performing a main scanning on the wafer in the X axis (or Y axis) direction and a subscanning thereon in the Y axis (or X axis) direction, and an inspection device in which a surface defect is inspected after performing shading correction for the line sensor.
2. Background Art
The wafer extraneous substance inspection device, which is a surface defect inspection devices, includes two types: one is an XY scanning type in which a laser beam is irradiated over the surface of a wafer in the X and Y axis directions to scan the surface of the wafer, and the other is a rotary scanning type in which a wafer is rotated and a laser beam is irradiated over the surface of the rotating wafer to scan the surface of the wafer in a spiral or concentric circle shape.
In accordance with an improvement in integration degree for ICs, an improvement in inspection accuracy for a wafer recently has been demanded. Therefore, the wafer extraneous substance inspection device of the XY scanning type tends to be employed for the extraneous substance inspection. However, when the XY scanning type is employed as an in-line extraneous substance inspection device which is brought into a semiconductor manufacturing process to perform extraneous inspection, through-put for the inspection is reduced, and a problem arises that the device tends to be bulky.
As a countermeasure, which eliminates such drawbacks, improves the through-put of the inspection and reduces the size of the device, the present assignee has filed a U.S. patent application Ser. No. 08/678,069 in which long and narrow inspection regions are set in the subscanning direction, a main scanning for on-going is performed in a single axial direction with a large scanning width, and another main scanning for returning is performed after turning a wafer by 180.degree..
However, when setting the long and narrow regions in the subscanning direction as explained above in order to improve the through-put in the inspection, CCD sensors covering, for example, about 1,000.about.10,000 pixels are needed for a line sensor (unidimensional image sensor). Moreover, when such long and narrow light receiving elements are used, light receiving sensitivities for respective unit pixels are different and shading (difference in detection level due to difference of detection pixels) is generated in extraneous substance detection signals which prevents a further accurate extraneous substance detection. In particular, in a case that the size of extraneous substances is determined depending on the level of the detection signals, the shading of the optical sensor is a significant problem.
In a conventional shading correction method for light receiving signals from respective pixels in a wafer extraneous substance inspection device using CCD sensors, a wafer having a predetermined standard particle (such as a projection at a predetermined position on a wafer is used as a standard particle) is moved in a main scanning direction to thereby move the predetermined standard particle along the arrangement direction of the CCD sensors and to detect the standard particle therewith. Thereafter, the shading correction is performed so that the detection outputs for the respective pixels assume the same output value. However, in the CCD sensor setting a long and narrow inspection region in the subscanning direction as mentioned above, the main scanning direction does not correspond to the movement of the CCD sensors along the pixel arrangement direction. Moreover, since movement in the subscanning direction which runs along the pixel arrangement direction is effected with a predetermined width, it is impossible to obtain accurate detection values for the respective pixels from the predetermined standard particle over the long distance along the arrangement direction of the CCD sensors.
As a result, since it is impossible to obtain shading correction values for respective detected pixels based on the detection values for the corresponding pixels as in the conventional manner, it is difficult to perform shading correction for the CCD sensors arranged in the subscanning direction in the above mentioned type of devices.